ed25519: make consts an alias for crypto/ed25519

This is a follow-up to Change-Id: I860ed963a0660753d01c89014c21360b239a38ac
(commit 20e1d8d), which dropped compatibility
with go1.12, and made this package an alias / wrapper for crypto/ed25519 in
stdlib.

While the above change aliased types and created wrappers for functions, it left
out the consts. I looked at the code review and commit message on that change,
but did not find a specific reason to leave these out. This patch updates the
consts to be an alias as well, which should make it even more transparent that
this package is an alias.

ed25519/ed25519.go

@@ -23,13 +23,21 @@ import (
 
 const (
 	// PublicKeySize is the size, in bytes, of public keys as used in this package.
-	PublicKeySize = 32
+	//
+	// This const is an alias for [crypto/ed25519.PublicKeySize].
+	PublicKeySize = ed25519.PublicKeySize
 	// PrivateKeySize is the size, in bytes, of private keys as used in this package.
-	PrivateKeySize = 64
+	//
+	// This const is an alias for [crypto/ed25519.PrivateKeySize].
+	PrivateKeySize = ed25519.PrivateKeySize
 	// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
-	SignatureSize = 64
+	//
+	// This const is an alias for [crypto/ed25519.SignatureSize].
+	SignatureSize = ed25519.SignatureSize
 	// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
-	SeedSize = 32
+	//
+	// This const is an alias for [crypto/ed25519.SeedSize].
+	SeedSize = ed25519.SeedSize
 )
 
 // PublicKey is the type of Ed25519 public keys.